Chemistry pH of solution.

  • Thread starter tua28494
  • Start date
  • #1
10
0
Here is a problem I was working on but I do not have a solutions manual because Its an old text book. I would just like someone to look over my work.


Homework Statement


Calculate the pH of a 0.67 M NaClO solution.


NaClO -> Na+ + ClO-

ClO- + H2O -> HCLO + OH-

Kw = 1.0*10^-14
Ka HCLO = 3.5*10^-8

Could you please check if these constants are correct.

Homework Equations



Kb = Kw/Ka HCLO

pH = -log [H+]


The Attempt at a Solution



Kb = Kw/Ka HCLO = 1.0*10^-14/3.5*10^-8 = 2.86 * 10^-7

With Kb we can solve concentrations for OH-

Kb = [HClO] [OH-] / [ ClO-]
2.86 *10^-7 = (x)(x) / (0.67-x) Quadratic Formula
x = 4.38 * 10 -4 M
[OH-] = 4.38 * 10^-4 M

[H+] [ OH-] = 1.0 *10^-14
[H+] = 1.0 *10^-14 / 4.38 * 10^-4 M
= 2.28 * 10^-11 M

pH = - log[H+]
= - log( 2.28 * 10^-11)
= 10.64


This is a reasonalbe result.

My last question is how do I turn off overtype when I am preparing a new thread?
Thank you for your time.
 

Answers and Replies

  • #2
Borek
Mentor
28,870
3,425
Looks OK. My sources give pKa for hypochlorous acid as 7.53.

My last question is how do I turn off overtype when I am preparing a new thread?

No idea what you mean.

--
methods
 
  • #3
10
0
So if the pKa is 7.53 should I use a different Ka?
 
  • #4
Borek
Mentor
28,870
3,425
Not necesarilly. These values quite often differ between sources. If you are given pKa value, use it in calculations. If you ask for help and ask others to check your results - list pKa value that you used.

--
methods
 
  • #5
10
0
I agree thank you
 
  • #6
4
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I think what she means by overtype is, when typing out a post, if you need to go back and make a correction to what you typed your correction eats away your typed text.

For your information, I had the same problem and came looking here for an answer, then I realized that my problem had been fixed. After some cursory exploration, I found that there is an "Insert" key on my keyboard right next to my left arrow key, that turns on overtype. Hit it again to turn it off.
 

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